In recent years, attempts have been made to incorporate religion into tobacco control efforts, especially in countries like Malaysia and Thailand where religion is central to the lives of people. This paper is a prospective examination of the perceived relevance and role of religion and religious authorities in influencing smoking behaviour among Muslims in Malaysia and Buddhists in Thailand. Data were collected from 1482 Muslim Malaysian and 1971 Buddhist Thai adult smokers who completed wave 1 (early 2005) of the International Tobacco Control Southeast Asia Survey (ITC-SEA). Respondents were asked about the role of religion and religious leadership on smoking at Wave 1 and among those recontacted, quitting activity at Wave 2. Results revealed that over 90% of both religious groups reported that their religion guides their day-to-day behaviour at least sometimes, but Malaysian Muslims were more likely to report that this was always the case. The majority (79% Muslims and 88% Buddhists) of both groups believed that their religion discourages smoking. About 61% of the Muslims and 58% of the Buddhists reported that their religious leaders had encouraged them to quit before and a minority (30% and 26%, respectively) said they would be an influential source to motivate them to quit. Logistic regression models suggest that these religious factors had a clear independent association with making quitting attempts in both countries and this translated to success for Malaysian Muslims but not for the Thai Buddhists. Taken together, results from this study indicate that religion and religious authorities are both relevant and important drivers of quitting, but whether this is always enough to guarantee success is less clear. Religion can be a culturally relevant vehicle to complement other tobacco control efforts.